The present invention relates to seating and more particularly to a chair for general office use.
Many office chairs have a seat portion and a back portion which tilts or reclines relative to a fixed base or support pedestal. This reclining action is accomplished by widely varying approaches, both structurally and philosophically. Relatively simple approaches, which include a chair control and a seat and back joined as a rigid unit, do not consider the natural motions and movement of the human body. The user is required to adapt to the chair. However, one common goal in contemporary design of office seating is the comfort of the user from the perspective of enhancing or at least not degrading the performance of the user in accomplishing the tasks of the office. With such attention directed to the performance of the user, interest has turned to the study of ergonomics in office seating. With the realization and development of ergonomics, a seating designer will endeavor to adapt the chair to follow the natural movement of the user. This can and has lead to sophisticated and complicated constructions which are correspondingly difficult and expensive to manufacture.
Ergonomics has led designers of office seating to focus on the natural and beneficial movements and positioning of a chair user and specifically the user's hips. The hip joints of an average user, seated upright with good posture in a chair, normally lie along an imaginary, generally horizontally oriented axis approximately 3 to 4 inches above the seating surface of the chair and approximately 3 to 5 inches forward of the plane of the chair back. The location of this hip joint axis in side elevational view with respect to a chair is generally referred to as the "H" point. Although the "H" point varies from one individual to another, depending upon the specific physical characteristics of the user, a model or preferred "H" point can be derived empirically, based upon studies of a wide range of different users. The "H" point is significant in ergonomic chair design because a user tends to rotate or roll the pelvis about the "H" point when moving from an upright or task position to a reclined or rest position. Therefore, it is desirable to approximate the "H" point axis in the construction of a chair recline control.
One chair structure responsive to ergonomic chair design and which attempts to approximate the "H" point axis incorporates a synchrotilt-type mechanism. In the synchrotilt mechanism, the seat portion of a chair moves in synchronization with the tilting of the back portion of the chair.
One such chair is disclosed by Linguanotto in U.S. Pat. No. 4,685,730, entitled SEAT, ESPECIALLY WORK SEAT, WITH SEVERAL POSITIONS, issued on Aug. 11, 1987. Linguanotto uses a three-piece seating cushion wherein a front seating portion is pivotally connected to a chair base and to a rear seating portion. The rear seating portion is hingedly connected to a back portion and is supported by a tilt bracket. The tilt bracket is a part of a chair control and is pivotally connected relative to the base. The back portion is also pivotally connected to the bracket.
Another synchrotilt chair is disclosed by Shields in U.S. Pat. No. 4,979,778, entitled SYNCHROTILT CHAIR, issued on Dec. 25, 1990. The Shields chair has separate seat and back portions with the seat portion connected to a chair base, at a front area of the seat portion, by a double pivot link. The seat portion is also pivotally connected to the back. The back portion is connected to a tilt control. When the back reclines, the rear of the seat portion moves rearwardly and downwardly, and the front of the seat portion moves rearwardly and downwardly lowering overall seat height.
Knoblock et al. disclose another synchrotilt chair in U.S. Pat. No. 4,776,633, entitled INTEGRATED CHAIR AND CONTROL, issued on Oct. 11, 1988. Knoblock et al. disclose the use of a structural shell having a seat portion and a back portion for use with a tilt mechanism. The back and seat portions are interconnected for mutual rotation about a common axis located above the seat portion and generally adjacent the hip joints of the seated user. A chair control supports the back and seat portions so that tilting of the back shifts the seat portion and the location of the common axis.
Yet another synchrotilt chair is disclosed by Franck et al. in U.S. Pat. No. 4,451,085, entitled CHAIR, issued on May 2, 1984. This chair uses a seat portion and a back portion which are interconnected by a flexible intermediate portion to accommodate changes in angle between the back and seat portions, when the back reclines. The seat portion is pivotally connected to a chair base, near a front edge of the seat portion. The back portion is connected to the chair base by a link which is pivotally connected at the back portion and pivotally connected at the base.